The fabrication of semiconductor devices is an important part of manufacturing many consumer products, such as cell phones, personal computers and numerous other products. In fabricating the semiconductor wafers, metals, chemicals and other materials are applied to the wafers in many layers in order to generate a variety of different devices on the wafers. One of the more expensive materials applied to the wafers is photoresist, which allows lithography to be used to etch other types of layers on the wafers.
Conventional methods for applying material to the semiconductor wafers have many disadvantages associated with them, especially for materials such as photoresist that can react with air. Crystallization of the material caused by such reactions is a major source of debris when the material is applied to the wafers.
As technology improves, the minimum size of the line widths that may be etched in the semiconductor wafers continues to decrease. As the line widths decrease, the size of debris that is acceptable also decreases. Eventually, the line widths may become so small that the debris may become a limiting factor. Thus, line widths that actually may be implemented will be determined by the debris size, regardless of whether or not it would be physically possible to etch smaller line widths if the debris were eliminated. Thus, minimizing or eliminating the debris is becoming more and more important in the fabrication of semiconductor wafers.
For the application of many materials onto the wafers, a pump is stroked to force an adjustable volume through a dispense nozzle by way of approximately ten feet of specialty Teflon-type tubing. After each dispense of the material, a suck-back force may be applied to draw the material away from the nozzle edge. This technique is typically used for materials such as photoresist that are prone to crystallization due to contact with the atmosphere. However, although this suck-back force may reduce crystallization, it fails to eliminate crystallization as a source of debris. In addition, conventional application methods include many other sources of debris that are unaffected by the use of a suck-back force.
Disadvantages associated with conventional application methods also include the fact that many materials, such as photoresist, are supplied in bulk containers. As a result, any contamination renders the whole batch unusable. Another disadvantage is that pumps typically incorporate a flexible bellows that comes in contact with the material itself, which results in another source of contamination as the material is flexed during each dispense and suck-back cycle. Also, the pump must be maintained, repaired and adjusted to provide the correct dispense volume for each wafer. Problems with incorrect volume can lead to scrap, rework and/or excess cost and disposal fees associated with the effluent material that is spun off the wafer during the thickness control (spin) function.
Disadvantages also include the use of the Teflon-type tubing line that transports the pump output up to the nozzle. Fixing a dispense contamination event sometimes involves replacing a contaminated line. In addition, the nozzle itself may become damaged in such a way as to shed metal debris onto the wafer or may become contaminated with crystallized material. Conventional application methods dispense some of the material onto dummy wafers in an attempt to avoid introducing any crystallized material when a dispense has not been performed within a relatively short amount of time, such as approximately 30 minutes. However, there is no algorithm for determining how many dummy wafers should be used to guarantee that the debris is flushed out. This method also results in the waste of the material that is used on the dummy wafers. In addition, the dummy wafers must then be cleaned off or discarded, further increasing production costs.
Another disadvantage associated with conventional methods for applying material to wafers is that the material in the bulk containers may be depleted without an operator being able to determine that the material is gone. In this situation, the application process may continue without any material being dispensed. This results in semiconductor wafers being moved along in the production line without the appropriate material being applied.
Before undertaking the DETAILED DESCRIPTION OF THE INVENTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term “controller” means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future, uses of such defined words and phrases.